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					Westport Oil and Gas Co., L.P.

  Evaluation of Oil Reservoir
Characteristics To Assess North
Dakota Carbon Dioxide Miscible
      Flooding Potential

      Ralph Nelms    Westport Oil and Gas Co.

    Randy Burke   North Dakota Geological Survey




                             North Dakota Geological Survey Geologic Investigations Number 21   1
        North Dakota CO2
         Mini-Test Pilot

• 1981 Gulf Oil Company.
• Little Knife North Field .
• Five Acre 5 Spot.
• Mission Canyon Formation.
• Recovered 13% of OOIP.
• MMP 3,100 psi.
• Gulf Projected Recovery of 8% of OOIP
 on 160-acre Well Spacing.
                                          2
      Previous North Dakota CO2
               Studies

• 1988 and 1990 Basin Electric Cooperative.
• North Dakota and Montana 26 Fields.
• 4,467 MMbo In Place.
• 858 MMbo Produced as of 1988.
• 1,038 MMbo Primary + Sec. EUR (~24% OOIP)
• 3,549 MMbo Remaining In Place
• 232 MMbo Potential CO2 Flooding Recoverable.
 (5.2% of OOIP)

                                                 3
       Dakota Gasification Co. CO2
           Pipeline Location



  CANADA

M.T.       N.D.




                             CO 2 PIPELINE



                                             4
        CO2 Screening Methodology
• Empirical reservoir characteristics.
• Analog dimensionless models (Shell Morgan
    Kinder).
•   Preliminary reservoir simulation studies (IFLO).
•   PVT tests, core analysis and core floods.
•   Advanced reservoir simulation studies
    (ECLIPSE,GEM, VIP)
•   Preliminary economic analysis.
•   Field pilot.
•   Large scale simulation and project economics.
•   Full scale development.                            5
          Favorable Reservoir
       Characteristics for Empirical
               Screening

• Reservoirs with good waterflood response are
    best Candidate for CO2. 20% OOIP< Recovery
    Factor <50% OOIP.
•   Depth >2500 ft to reach MMP.
•   Oil Gravity >27 Degrees API.
•   Oil Viscosity <10 cp.
•   Porosity >12%.
•   Permeability >10 md.

                                                 6
          Quick Rules of Thumb

•   Recovery factor using miscible CO2 is 8% -11%
    OOIP. Immiscible CO2 50% of miscible.
•   MMP equals initial bubble point pressure.
•   CO2 requirement is 7-8 Mcf/bo plus 3-5 Mcf/bo
    recycle.
•   Water injection required to fill gas voidage and
    increase reservoir pressure to original BHP.
•   WAG is alternative but 10 Mcf/bo still required.
•   Top down CO2 injection alternative is effective
    but requires more capital investment for higher
    CO2 volume.
                                                       7
         Unfavorable Reservoir
       Characteristics for Empirical
               Screening
• High concentrations of vertical fractures.
• Very high, or very low, permeability.
 (Vertical segregation or fracture channeling)
• Thick reservoirs with no layered horizontal
  permeability barriers.
• Reservoirs with poor connectivity.
• Well spacing >80 acres.
• Poor material balance during water flood. (High
  water loss out of zone, water influx or high water
  cut during primary production)
                                                       8
        U.S. Active CO2 Floods

• Texas             48 (26 Succ, 8 TETT, 13 Prom, 1 Fail)
• Wyoming            5 (5 Success)
• Oklahoma           4 (2 Success, 1 TETT, 1 Promising.)
• Utah               2 (1 Success, 1 Promising)
• Mississippi        2 (1 Success, 1 Promising)
• Michigan           2 (1 Success, 1 TETT)
• New Mexico         2 (1 Success, 1 Promising)
• Colorado           1 (1 Success)__________________
Total               66 (38 Success, 10 TETT, 17 Prom.)


* First CO2 Flood SACROC Jan 1972
                                                            9
       Summary of US CO2
       Active Floods (CEED 2002)


• Total Active CO2 Floods = 66
• Total Successful = 38
• Total Successful Carbonates = 29
• Total Successful Sandstones = 9
• Of 29 Successful Carbonate Units, 18 are
 in San Andres Dolomite.


                                             10
          Reservoir Characteristics
         of 29 Successful Carbonate
               CO2 Floods 2002


US Average                               North Dakota Madison
• Porosity       11% (7%-13.5%)              10.9%
• Permeability   9 Md (1.5-62)               10.2 Md
• Depth           5,281 feet (4500-8000)      7,500 feet
• API            33 degrees (28-41)           38.7 degrees
• BHT             108 degrees F (86-134)      201 degrees F
• Viscosity       1.52 cp (0.5 –2.6)          1.54 cp

So at start of CO2 flood = 55% (35%-89%)

                                                                11
     Reservoir Parameters of
      Carbonate CO2 Floods


Well Spacing for 38 Successful CO2 Floods:
   1 Field at 130 acres
   2 Fields at 75 acres
   2 Fields at 50 acres
   32 Fields < 40 acres
38 Well average was 27.6 acres


                                             12
                              Porosity and Permeability
                              North Dakota Madison Vs.
                             Texas San Andres Formation

                    80
                                                       North Dakota Madison
                    70
Permeability (md)




                    60                                 Texas San Andres
                    50
                    40
                    30
                    20
                    10
                     0
                         0     5       10          15         20          25
                                        Porosity (%)

                                                                               13
          Favorable Reservoir
        Characteristics for North
      Dakota Carbonate Reservoirs



• MMP is Easily Achievable
 Depth, API Gravity and BHT all Favorable for CO2 Flooding.
• Porosity, Permeability and So are all within Range of other
 Successful Carbonate Reservoirs.
• H2S in Sour Crude in not a constraint.
• Deeper Reservoirs offset Higher BHT for MMP


                                                                14
             Unfavorable North Dakota
             Reservoir Characteristics



•   Large Well Spacing averages 160 acres.
•   Many Reservoirs are Vertically Fractured.
•   Depth Increases Well Costs for Infill Drilling New Wells : $100/ft
•   Sour Gas Recycling Costs.
•   Heterogeneity limits sweep efficiency.




                                                                     15
         Weyburn CO2 Project,
        Saskatchewan, Canada
• Started in 2000. $1.3 billion Encana project. $100
  million DGC project. 25 year life.
• 1,300 MMbo in place. CO2 recovery 130 MMbo.
  10% OOIP from CO2 flood.
• 723 wells, 179 horizontal, 221 injection.
• Injecting 70-90 MMcfpd CO2.
• 95% Quality CO2 from Great Plains in Beulah. 198
  mile pipeline
• 4,655’ deep. 10’-89’ thick. Sour 25-35 API gravity.
• Vuggy Limestone: 15% porosity 30 md.
• Marly Dolomite: 26% porosity 10 md.
• SSWAG injection due to fractures.                     16
                 CO2 Reservoir Excel
                      Database
NDIC Derived Data           Author’s Data Input
Unit Name/ Pool/ OOIP      CO2 Oil Recovery (8% OOIP)
Peak Rates,                CO2 Oil Reserve Category
Primary EUR, RF            Favorable/Unfavorable
Secondary EUR, RF          CO2 Flood Characteristics
Unit size                  Porosity, Permeability, Boi
Effective Date             uo, uw, M, h, BHT, API, Rw
                           WOR, Soi, Soirr Swirr,
                           P*, Pbp, Non-Unitized Fields
                           Distance to CO2 Pipeline,
                           Fracture Description
                                                          17
            North Dakota Highest
          Ranked Reservoirs for CO2
                  Flooding



• Mississippian -Madison Group   • Devonian - Duperow
    Mission Canyon              • Permian/Triassic -Spearfish
    Glenburn                    • Pennsylvanian -Tyler “Health”
    Sherwood
    Ratcliffe




                                                                   18
 North Dakota Lowest Ranked
 Reservoirs for CO2 Flooding



•Silurian - Interlake
•Devonian - Winnipegosis
•Madison with Cross-seal Fractures
•Ordovician - Red River B with Cross-
 seal Fractures

                                        19
        CO2 Potential Oil Reserve
             Classification

• Probable, Possible, Unfavorable
• Probable (>2MMbo and <2MMbo):        Highest
    probability of success based upon empirical
    analysis and comparison to other successful
    projects.
•   Possible (>2MMbo and <2MMbo): Feasible but
    have less favorable reservoir characteristics. May
    have lower oil recovery.
•   Unfavorable: Significant reservoir problems.
•   Projects with greater than 2 MMbo recoverable
    best candidates.
                                                         20
     Probable Top Ten North Dakota
         Units for CO2 Flooding

• Beaver Lodge - Madison          17.6 MMbo
• Tioga - Madison                 17.2 MMbo
• Big Stick - Madison             13.3 MMbo
• Fryburg - Heath (Tyler)          12.4 MMbo
• Beaver Lodge - Devonian          11.1 MMbo
• Newberg - Spearfish & Charles    7.7 MMbo
• Wiley - Glenburn                 7.6 MMbo
• Blue Buttes - Madison            7.4 MMbo
• North Tioga - Madison            7.2 MMbo
• Charleson North - Madison         6.4 MMbo
                                               21
         Possible Top Ten North
          Dakota Units for CO2
                Flooding
• Cedar Hills South - RRB           28.8 MMbo
• Cedar Hills North - RRB           22.2 MMbo
• Antelope - Madison                8.0 MMbo
• Cedar Creek - Ordovician          7.7 MMbo
• Medicine Pole Hills West - RRB    3.4 MMbo
• Medicine Pole Hills - RRB         3.2 MMbo
• Medicine Pole Hills South - RRB   3.1 MMbo
• Eland - Lodgepole                 2.8 MMbo
• Lignite - Madison (PA)            2.6 MMbo
• Rough Rider East- Madison         2.3 MMbo
                                                22
Unfavorable North Dakota
 Units for CO2 Flooding



 • Horse Creek Red River
 • Red Wing Madison
 • Fryburg Madison
 • TR Madison (South)


                           23
         Constraints to North Dakota
             CO2 Development

• Most oil reservoirs are 7,500 feet and many have well spacing >80
 acres requiring high cost infill drilling.
• Only Nesson Anticline fields are less than 10 miles to existing
 CO2 pipeline. Fields not on the Nesson anticline will be burdened
 with large pipeline installation costs.
• Most existing waterflood units are in mature waterflood stages at
 high water cuts.
• Low permeability and highly heterogeneous.
• Many reservoirs have strong water influx from vertical fractures
 outside of pay zone boundaries.

                                                                      24
                    Conclusions

•   55 fields in North Dakota have Probable CO2 recoverable
    reserves of 171 MMbo.
•   26 fields in North Dakota have Possible CO2 recoverable
    reserves of 106 MMbo.
•   One successful CO2 pilot has been conducted to date.
•   Comparison of North Dakota reservoir characteristics to
    successful Texas and Canadian reservoirs utilizing CO2
    flooding is favorable.
•   Future North Dakota CO2 development constraints are
    principally economic and will require large capital
    investments over long time periods plus the ability to
    manage both oil price and CO2 price risks. A long term
    economic perspective will be required since CO2 projects
    require long payouts on investment.
                                                               25

				
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